The light conditions at the sediment surface was determined by a natural layer of seafoam covering the water surface. Three scenarios were investigated: 1) no foam, 2) little foam, and 3) thick foam. Light was measured at the sediment-water interface.Instrumentation : Optode microprofiling device from PreSens GmbH (Germany, www.presens.de) with an Automated Micromanipulator (AM) and needle-type optodes for measurements of oxygen (PM-PSt7). Temperature and light was measured at the sediment-water interface with HOBO Pendant© Temperature/Light Datalogger.Time: July 2018.Depth "0" is defined as the top of the microphytobenthos layer at the sediment-water interface.Salinity (‰): 39.Temperature (°C): 33.2.